The present invention relates generally to hand tools and, more particularly, to a hand tool with jaws and a force-multiplying mechanism, and, still more particularly, to a mechanism for adjusting the force-multiplying mechanism and the jaws of the tool. The adjustment mechanism may be used to adjust the force-multiplying mechanism and the fit of the jaws to accommodate wear, to adjust the interaction of the jaws, or for other purposes.
In the field of hand tools, many tools include a pair of jaws that are pivotally connected to one another. The jaws are connected to handles that may be grasped by a user. The user exerts force on the handles to rotate the jaws toward each other, allowing the jaws to exert a compressive force on each other. The jaws may be adapted for cutting, crimping, or other purposes.
Some tools with jaws—for example, certain bolt cutters and crimpers—have compound mechanisms for aiding the user in applying large compressive forces between the jaws. In this class of tools, the handles of the tool are not attached directly to the jaws, and the jaws may or may not be pivotally attached directly to each other.
Referring to FIGS. 10 and 11, an exemplary tool according to the prior art has a pair of handles 414 attached to the input ends 324a, 342a of a pair of shrouds 324a, 342b, which are generally trough-shaped or U-shaped members. The output ends 324b, 342b of the shrouds 324, 342 are pivotally connected to and exert output forces upon the actuator arms 320, 322 of the jaws 314, 316. The jaws 314, 316 are pivotally attached to one another by a pivoting connection 318 as shown in FIG. 10 or alternatively are each pivotally attached to a third member. The user exerts an input force on the handles 414 over a first distance by pushing the handles 414 toward one another. At the output ends 324b, 342b of the pivotally attached shrouds 324, 342, the force exerted by the user over the first distance is multiplied and becomes an output force greater than the user's input force and exerted over a second, smaller distance. The force from the output ends 324b, 342b of the shrouds 324, 342 is preferably further multiplied into an output force greater still than the output force of the output ends 324b, 342b of the shrouds 324, 342. In this manner, the compound mechanism transforms the user's input force into a compressive output force many times higher than the user's input force.
The prior art tool 310 includes a adjustment mechanism, which allows the user to adjust the force-multiplying mechanism and the fit of the jaws 314, 316 by means of an arm 360 pivotally attached to the actuator arms 320, 322 of the jaws 314, 316 and secured near one end by an adjustment screw 378, as shown in FIG. 10. The adjustment screw 378 has a threaded portion, which engages with a threaded bore 381 in the arm 360 (see FIG. 11) and which passes through an opening (not shown) in the surface 325 of the shroud 324. The adjustment screw 378 also has a screw head engaging a surface 325 of the shroud 324 to fix or constrain the relationship between the jaws 314, 316. In such a mechanism, the connection between the threaded portion of the screw 378 and the threaded bore 381 tends to move the screw 378 to make contact with the lowermost portion of the opening; and the screw head also tends to contact the surface 325 of the shroud 324 at an angle so that the screw head 325 is not parallel to the surface 325. Under these conditions, the screw 378 is loaded substantially in bending rather than in tension. As a result, a user may inadvertently place a high level of bending stress on the adjustment screw 378, resulting in failure of the screw 378. Moreover, some prior tools include two such adjustment mechanisms, and users may find prior tools difficult to adjust.
In certain embodiments, the presently preferred invention is a tool having a single adjustment mechanism that allows adjustment of the force-multiplying mechanism and jaws of the tool, preferably through the manipulation of a single screw. The mechanism improves upon the mechanism of the prior art by pivotally coupling the adjustment screw to the arm in a manner that differs from the prior art and that preferably serves to cause the adjustment screw to be loaded primarily in tension, with the bearing surface of the screw head generally parallel to the surface of the shroud, thus reducing the stress placed on the adjustment screw. As a result of the reduced stress and the loading of the adjustment screw primarily in tension, in certain embodiments of the invention, the life of the adjustment screw is five times the life of the adjustment screws in comparable prior-art devices.